Blends of rubbers and asphalt have been used in paving for years. One of the accepted methods of adding polymers to asphalt is by means of injecting latex, an aqueous dispersion of microscopic particles of polymer in water, into hot, liquid asphalt during the production of hot-mixed asphalt paving mixtures at a contractor's hot-mix asphalt plant. Although it has been known that there are advantages in using the rubber in the form of latex, there have been various drawbacks, perhaps the chief of which has been the fact that latex modified asphalt can have a significantly higher viscosity than conventional asphalt used for hot-mixed asphalt applications. The increased viscosity can be due to the swelling, that is, the partial solvating, of the polymer particles in the asphalt and the tangled network of polymer chains produced in the asphalt matrix. This phenomenon can require latex modified asphalt paving mixtures to be mixed and applied at higher temperatures than conventional hot-mixed asphalt pavements.
There is a need in the asphalt paving industry to lower hot-mixed asphalt paving mixing and application temperatures. This effort has resulted in a form of hot-mixed asphalt termed “warm mix”. Warm mix technology attempts to produce a similar product as conventional hot-mixed asphalt but which is mixed and installed approximately 60° F. lower than conventional hot-mixed asphalt pavements.
Several products and techniques have been promoted to achieve warm mix. They include injecting water directly into the asphalt, incorporating the use of zeolite that holds water and releases it slowly into the asphalt in the form of tiny droplets, adding a wax produced from the gasification of coal and the use of asphalt emulsions. These techniques and products are perceived to have limitations. The mechanism by which most of the warm mix products believably work is not to reduce the viscosity of the asphalt, but to form “slip planes” in the asphalt in the form of microscopic globules of substances which are non-solvent liquids at mixing temperatures for the asphalt. Globules are defined as liquid or liquid-like particles and non-solvent is defined as having no or very little ability to dissolve a substance in another substance. These non-solvent globules include water and waxes and other substances. The non-solvent microscopic globules believably allow sheer forces applied to the asphalt to deform the asphalt making it more “fluid” and easier to mix with aggregate at a lower temperature. This same phenomenon allows the paving mixture produced with these materials to be applied and compacted at lower temperatures as well. The volume of microscopic non-solvent globules required to produce warm mix varies but generally is in the range of 1% to 3% of the asphalt content.
U.S. Pat. No. 3,285,871 to Carlson relates to a disclosure wherein the water of the latex is replaced by a polyhydric alcohol, and this dispersion or latex is mixed with the bitumen. The dispersion or latex may be formed by evaporating the water of the latex under a vacuum and replacing it with the alcohol, or when the rubber is a synthetic polymer, such as dispersion of the polymer in the alcohol may be produced directly by carrying the polymerization out in the alcohol instead of in water. For certain latexes, it is necessary to increase the quantity of stabilizer over that required for an aqueous latex, in order to prevent coagulation during processing.